Estrogens are synthesized from androgenic steroids. In the biosynthetic pathway for estrogen formation, aromatization is an essential step. It is generally believed that if the aromatase enzyme could be effectively inhibited, a useful treatment for estrogen dependent disorders could be obtained (see Cancer Research, Vol. 42, Suppl. 8:3261s (1982)).
Several estrogen dependent diseases exist which could be treated with aromatase inhibitors. These include breast cancer, endometriosis, polycystic ovarian disease, benign breast disease, and endometrial cancer. A beneficial effect of antiestrogens in the treatment of breast cancer has been well established (see Br. J. Cancer, 25, 270 (1971)). Two of the known aromatase inhibitors, testolactone and aminoglutethimide, have shown a beneficial effect in treatment of breast cancer. See Cancer Research, supra.
Endometriosis is characterized by an abnormal proliferation of the endometrium of the uterus. Since the endometrium is dependent on estradiol for its growth, an inhibitor of estrogen production should stop the progression of the disease.
Benign breast disease, or often called fibrocystic breast disease, appears to be dependent on ovarian steroids. See Cancer, 49, 2534 (1982). Aromatase inhibitors have not been tried in this disease, but antiestrogens seem to be of benefit. See Obstet. Gynecol., 54, 80 (1979).
Polycystic ovarian disease is one of the most common causes of infertility in women. The disease appears to result from an abnormality in steroid metabolism, and the major form of therapy in this disease is the antiestrogen, clomiphene. See Clin. Endocrinol., 12, 1977 (1980).
It is the purpose of this invention to provide a method of inhibiting the enzyme aromatase in mammals employing certain pyrazine derivative. The invention thus provides for the treatment or prevention of breast cancer and other estrogen-dependent diseases.